The obesity epidemic has been linked to increasing incidence of diabetes, cardiovascular disease and other complications. Diet and exercise are essential to weight management;however, it is obvious that many patients would require drug treatment to achieve and maintain weight reduction. The goal of this grant is to understand the actions of a novel aminosterol, which we have found to potently decrease body weight. During the past 3 years, we have shown that the anti-obesity effect of MSI-1436 is mediated through inhibition of food intake as well as increased metabolic rate. Unlike other anorectics, a single intraperitoneal or intracerebroventricular (i.c.v.) injection of MSI-1436 decreases body weight for several days. Moreover, MSI-1436 stimulates insulin response and prevents steatosis. An intact leptin signaling is not critical to the action of MSI-1436, since this compound is effective in ob/ob and db/db mice, fa/fa rats, and diet-induced obese mice. In contrast, agouti (Ay/a) mice are less responsive to MSI-1436, suggesting that melanocortin (MC)3/4 receptors are crucial its action in the brain. MSI-1436 binds to hypothalamic and other brain areas which mediate energy balance, and strongly induces Fos-immunoreactivity in the paraventricular hypothalamic nucleus and to a lesser extent in the arcuate, ventromedial nuclei, central amygdala and nucleus solitarius. A CNS action of MSI-1436 is further evident by the suppression of agouti-related peptide (AGRP) and neuropeptide Y (NPY) in hypothalamus. Hence, we hypothesize that MSI-1436 regulates energy balance and glucose through similar hypothalamic circuits. Specific Aim 1 will investigate whether treatment with NPY or AGRP can reverse the effect of MSI-1436. Moreover, we will determine whether deletion of NPY, AGRP and MC4 receptor genes block the action of MSI-1436. Specific Aim 2 will investigate the roles of NPY, AGRP and MC4 receptor in mediating the effect of MSI-1436 on glucose. Specific Aim 3 will evaluate the effects of MSI-1436 on hypothalamic enzymes, i.e. AMP kinase and fatty acid synthase, implicated in energy homeostasis. Finally, specific Aim 4 will determine whether activation of hypothalamic AMP kinase is able to prevent the effect of MSI-1436, as has been shown for various anorectics. Understanding of the central neuronal actions MSI-1436 may elucidate novel targets for the treatment of obesity and related diseases.